More restrictive exhaust emissions laws for diesel and natural gas engines and high power output for internal combustion engines have driven changes in engine design including the need for high-pressure electronic fuel injection systems in diesel engines and stoichiometric combustion in natural gas engines. Engines built according to the new designs use higher combustion pressures, higher operating temperatures and less lubrication than previous designs. Components of the new designs, including valve seat inserts (VSI), have experienced significantly higher wear rates. Intake and exhaust valve seat inserts and valves, for example, must be able to withstand a high number of valve impact events and combustion events with minimal wear (e.g., abrasive, adhesive, and corrosive wear). This has motivated a shift in materials selection toward materials that offer improved wear resistance relative to the valve seat insert materials that have traditionally been used by the diesel and natural gas industry.
Another emerging trend in diesel engine development is the use of EGR (exhaust gas recirculation). With EGR, exhaust gas is routed back into the intake air stream to reduce nitric oxide (NOx) content in exhaust emissions. The use of EGR in diesel or natural gas engines can raise the operating temperatures of valve seat inserts. Accordingly, there is a need for lower cost valve seat inserts having good mechanical properties including hot hardness and compressive yield strength for use in diesel and natural gas engines using EGR.
Also, because exhaust gas contains compounds of nitrogen, sulfur, chlorine, and other elements that potentially can form acids, the need for improved corrosion resistance for alloys used in valve seat inserts is increased for diesel and natural gas engines using EGR. Acid can attack valve seat inserts and valves leading to premature engine failure.